[Feature Request][Debug info] Globals lowered to `global.<name>` locals should link to their declaring scope

[hbystuff]

Version: dxcompiler.dll 1.9(5402-0d3ee6b5)(1.9.0.5402) - 1.9.0.5402 (0d3ee6b55-dirty)

lowered_global.zip

Static globals are lowered to SSA values and mirrored into a synthetic
DILocalVariable named global.<name>. That variable is scoped to a function
subprogram and carries no reference to the declaring namespace or class, and no
link back to the DIGlobalVariable that does have the correct scope.

Repro 1: namespace

dxc -T cs_6_0 -Zi -Qembed_debug -Od -Fc namespace_static.ll namespace_static.hlsl

namespace A { static int MyNum = 67; }      // line 11
namespace B { static int MyNum = 68; }      // line 15

[numthreads(1, 1, 1)]
void main()
{
    A::MyNum = input[0];
    B::MyNum = input[1];
    output[0] = A::MyNum + B::MyNum;
}

Actual

!42 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "global.MyNum", arg: 0, scope: !4, file: !1, line: 15, type: !12)
!45 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "global.MyNum", arg: 0, scope: !4, file: !1, line: 11, type: !12)

!4 is the main subprogram for both, so A::MyNum and B::MyNum are
indistinguishable apart from line:.

The namespace is present elsewhere in the module, just not reachable from the
local:

!14 = !DIGlobalVariable(name: "MyNum", linkageName: "\01?MyNum@A@@3HA", scope: !15, file: !1, line: 11, ...)
!15 = !DINamespace(name: "A", scope: null, file: !1, line: 10)
!16 = !DIGlobalVariable(name: "MyNum", linkageName: "\01?MyNum@B@@3HA", scope: !17, file: !1, line: 15, ...)
!17 = !DINamespace(name: "B", scope: null, file: !1, line: 14)

Repro 2: class static member

dxc -T cs_6_0 -Zi -Qembed_debug -Od -Fc class_static_member.ll class_static_member.hlsl

class Counter
{
    static int count;
    int localValue;
    void Initialize(int value) { localValue = value; count += value; }
};

int Counter::count = 0;         // line 23

Actual

One global.count is emitted per function that touches the static, each scoped
to that function's subprogram:

!48 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "global.count", arg: 0, scope: !7, file: !1, line: 23, type: !11)
!51 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "global.count", arg: 0, scope: !4, file: !1, line: 23, type: !11)

!4 = !DISubprogram(name: "main", ...)
!7 = !DISubprogram(name: "Initialize", linkageName: "\01?Initialize@Counter@@QAAXH@Z", scope: !8, ...)

call void @llvm.dbg.value(metadata i32 0,  i64 0, metadata !48, metadata !49), !dbg !50   ; var:"global.count" !DIExpression() func:"Initialize"
call void @llvm.dbg.value(metadata i32 0,  i64 0, metadata !51, metadata !49), !dbg !52   ; var:"global.count" !DIExpression() func:"main"
call void @llvm.dbg.value(metadata i32 %6, i64 0, metadata !48, metadata !49), !dbg !50   ; var:"global.count" !DIExpression() func:"Initialize"
call void @llvm.dbg.value(metadata i32 %6, i64 0, metadata !51, metadata !49), !dbg !52   ; var:"global.count" !DIExpression() func:"main"

Expected

There should be a way to link a global lowered to local back to the original global, something like:

!dx.dbg.local_globals = {!100, !101}

!100 = !{ !48, !23 }
!101 = !{ !51, !23 }
!8  = !DICompositeType(tag: DW_TAG_class_type, name: "Counter", file: !1, line: 11, size: 32, align: 32, elements: !9)
!10 = !DIDerivedType(tag: DW_TAG_member, name: "count", scope: !8, file: !1, line: 13, baseType: !11, flags: DIFlagPublic | DIFlagStaticMember)
!23 = !DIGlobalVariable(name: "count", linkageName: "\01?count@Counter@@2HA", scope: !0, file: !1, line: 23, type: !11, isLocal: true, isDefinition: true, declaration: !10)
!48 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "global.count", arg: 0, scope: !7, file: !1, line: 23, type: !11)
!51 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "global.count", arg: 0, scope: !4, file: !1, line: 23, type: !11)

So the backend can reconstruct the correct scope information if appropriate.